The functional films used to coat ophthalmic lenses are sometimes flat in their initial state, for reasons of ease of manufacture of these films; methods for gluing an initially flat functional film to a curved face of a substrate are already known.
In these methods, to prevent defects appearing in the film, the film is preformed using a cold, or preferably hot (thermoforming), method to give it an appropriate initial curvature, before being applied to the substrate.
In particular, French patent application 2 883 984, to which U.S. 2008/0314499 is the corresponding United States patent application, proposes positioning the substrate having a curved face on a substrate holder inside a chamber; positioning the flat functional film on a film holder at the upper end of the chamber in order to close this chamber; positioning the chamber vertically in line with a flexible buffer so that their respective geometric centres are aligned; preforming the functional film by applying the flexible buffer to the film; creating a negative pressure in the chamber, this negative pressure causing the substrate and the functional film to move so that their respective geometric centres make contact on the curved-face side of the substrate; and translating the flexible buffer vertically so as to establish a conformal contact between the functional film and the substrate on the same side as its curved face.
French patent application 2 918 917, to which U.S. 2010/0193112 is the corresponding United States patent application, proposes to implement a similar gluing method, but in which the direct immobilization of the film by the film holder along an annular perimeter is replaced by immobilisation of an initially flat deformable auxiliary membrane, on one face of which the functional film is retained by a binding layer configured so that the shape of the functional film varies conformally to the deformation of the membrane, the functional film then remaining parallel to the auxiliary membrane, only the auxiliary membrane being held by the film holder at its perimeter, the functional film being held in contact with the auxiliary membrane only by the binding layer.
The implementation of the gluing method described in French patent application 2 918 917 is carried out:                as in French patent application 2 883 984, i.e. a flexible buffer is used to preform the functional film, giving it a curvature the convexity of which is turned towards the curved face of the substrate; the centre of the convex face of the functional film is brought into contact with the centre of the convex curved face of the substrate; and then the functional film is applied with the flexible buffer by inverting its curvature in order to diffuse radially from the centre of the functional film as far its periphery the conformal contact between the functional film and the substrate; or        as a variant, a flexible buffer is not used and the negative pressure in the chamber is replaced by a positive pressure that is used to preform the functional film, thereby giving it a curvature the concavity of which is turned towards the curved face of the substrate; the centre of the concave face of the functional film is brought into contact with the centre of the convex curved face of the substrate; and then the film is applied, without inverting its curvature, by driving the substrate towards the film, in order to diffuse radially from the centre of the film as far as its periphery the conformal contact between the functional film and the substrate.        
In the gluing method described in French patent application 2 918 917, since the functional film is not held at all at its periphery by mechanical means, it can slide over the membrane while the deformation is generated, thus decreasing the strains that are created in the functional film.
Moreover, it is known that functional films can be used to provide a very wide range of functions, for example an anti-shock function, an anti-scratch function, an anti-reflection function, a polarising function, a colour-filtering function, a photochromic function, an antistatic function or an anti-smudge function.